Charged particle beam spreader system including three in-line quadrapole magnetic lenses



R SYSTEM lNcLUDI 3 Sheets-Sheet 1 umm INVENTOR JOHN c. HERR RA BY mm)f/"m ATTORNEY Dec. 2, 1969 .1.c. HERRERA CHARGED PARTICLE BEAM SPREADTHREE IN-LINE QUADRAPLE MAGNETIC LENsEs Filed April 13, 1966 Dec, 2,1969 J. c. HERRERA 3,482,135

CHARGED PARTICLE BEAM SPREADER SYSTEM INCLUDING THREE IN-LINE QUADRAPLEMAGNETIC LENSES Filed April 1s, 196e s sheets-sheet s INVENTOR JOHN C.HERR RA BY AORNEY United States Patent O 3,482,136 CHARGED PARTICLE BEAMSPREADER SYSTEM INCLUDING THREE IN-LINE QUADRAPOLE MAGNETIC LENSES JohnC. Herrera, Stoneham, Mass., assgnor to High Voltage EngineeringCorporation, Burlington, Mass., a corporation of Massachusetts FiledApr. 13, 1966, Ser. No. 542,276 Int. Cl. Hh 7/04 U.S. Cl. 313-63 2Claims ABSTRACT OF THE DISCLOSURE An apparatus for projecting andenlarging charged particle beams comprising a particle beam generatorand accelerator feeding the beam through an aperture to a gradient lenssystem, composed of three in-line quadrapole lenses, which focuses it ata cross-over point such that the beam after passing the cross-over pointexpands uniformly to form a greatly enlarged distortion free image ofthe aperture.

This invention relates to charged particle beam manipulation and inparticular to an apparatus for projecting and enlarging charged particlebeams.

Charged particle beams of energies below 1 Bev. are being increasinglyused in many diverse tields such as radiation chemistry and cosmic spacesimulation.

At present, the devices used for manipulation of these beams are capableonly of either moving the beam from spot to spot, such as in theso-called flying spot scanners, or line by line such as shown in PatentNo. 2,866,903, dated Dec. 30, 19'58, entitled Method of an Apparatus forIrradiating Matter with High Energy Electrons, issued to John Nygard.

Although the above described equipments are quite adequate for manysituations, they fail in others. One typical application in which priorart devices are not adequate is in space radiation simulation in whichit is necessary that a large body such as a space satellite be exposedto a high energy radiation ield. Since such satellites usually depend onlarge numbers of potentially radiation sensitive, electronic circuits,it is necessary that such devices be tested by exposure to a radiationfield such as may be encountered in interplanetary space.

In order to overcome the deliciencies encountered when using line orspot irradiation in such applications the present invention wasconceived.

Broadly speaking the present invention is directed towards a chargedparticle beam manipulation device capable of simultaneously irradatingthe entire exposed surface of a body and accomplishes this feat bypassing a charged particle beam through a plurality of suitably disposedmagnetic lenses capable of projecting and enlarging the beam through asignificant solid angle.

The invention will be better understood in detail by reference to thefollowing description when taken in conjunction with the accompanyingillustrations of a speciiic embodiment thereof.

In the drawings:

FIGURE l is an overall view of the apparatus;

FIGURE 2 is a broken away view of the preferred lens system used in theapparatus of FIGURE l;

FIGURE 3a shows the lield configuration of the central lens of thesystem shown in FIGURE 2;

FIGURE 3b shows the field configuration of the end lenses of the systemshown in FIGURE 2;

FIGURE 4a shows the particle trajectory in the Y plane of the lenssystem of FIGURE 2;

FIGURE 4b shows the particle trajectory in the X plane of the lenssystem of FIGURE 2;

3,482,136 Patented Dec. 2, 1969 lCC FIGURE 5a shows the beam pattern ofthe apparatus of FIGURE 1 in the Y plane;

FIGURE 5b shows the beam pattern of the apparatus of FIGURE 1 in the Xplane.

Referring now to the drawing and more particularly to FIGURE l, there isshown a charged particle apparatus 10 which is capable of forming ahighly energetic charged particle beam 11, accelerating the beam,directing it along the center of an evacuated drift tube 13, through adeiining aperture 14 and a gradient lens system 15 into an evacuatedradiation chamber 16 in which there is positioned a device 17 which isto be irradiated. To provide uniform irradiation of the entire devicesurface, the device 17 is preferably rotatably supported in the chamber16 by any suitable means (not shown).

In accordance with the invention when the beam passes through aperture14, it is defined so that it is tight and uniform as it enters the lenssystem 15. As the beam passes through the lens system, it issuccessively manipulated in both the Y and Z planes such t at the beambecomes concentrated at a cross-over point 35 posterior to the lenssystem. Upon passing this cross-over point the beam expands in alldirections into an enlarged image of aperture 14.

The lens system 15, preferably used in the present invention, is atriplet quadrapole magnetic system and is shown in detail in FIGURE 2.This lens system comprises three quadrapole lenses 20, 21 and 22 all ofWhich are maintained in line and enclosed in a single housing 24. Eachlens consists of four pole pieces and surrounding electromagnetic coils.When power is supplied to the coils, the pole pieces become magnetizedand a magnetic ield is established between the faces of the respectivepole pieces.

Because quadrapole magnets by their nature converge a charged particlebeam passing therethrough in one direction while diverging it at rightangles to the converging direction, it is necessary that each lens 20,21 and 22 be arranged in such a manner that the beam passingtherethrough will converge, in both the X and Y planes, at thecross-over point 35. This can be fully appreciated from a review ofFIGURES 3a, 3b, 4a and 4b which show the magnetic fields which must beset up in each lens and the lbeam trajectories required in both theconverging and diverging planes of each lens. This is accomplished byrotation of polarity of each end lens with respect to the central lensand by making the length of the central lens 20 twice that of the endlenses 21 and 22. This rotation of polarity of the end lenses 21 and 22with respect to the control lens 20 is achieved by exciting the coils29a and 31a of central lens 20 such that pole pieces 25a and 27a aresouth poles, while energizing coils 30a and 32a such that pole pieces26a and 28a are north poles and simultaneously energizing both sets ofcoils 29b and 31b and 30b and 32b, of end lenses 21 and 22, such thatpole pieces 26b and 28b are south poles and 25b and 27b are north poles.

The above described arrangement of the triplet quadrapole lens systemwill condense the beam at the cross-over point 35 and impart to theparticles comprising the beam a direction such that a greatly enlargedreproduction of image 14 is produced at the end of chamber 16.

Since the beam expands uniformly in both the X and Y directions after itpasses the cross-over point 35, an object placed in chamber 16, ifsmaller than the expanded beam, will have its surface uniformlyirradiated. The chamber 16 can be lengthened to any desired size limitedonly by mechanical and vacuum considerations.

It should, of course, now be obvious to those skilled in the art thatthe triplet lens described above may be replaced with an equivalent suchas two, in line, quadrapole doublets.

Since other variations and modifications of the present invention maynow become apparent to those skilled in the art, it is desired that thedescribed invention be limited only by the following claims.

What is claimed is:

1. A beam enlargement apparatus for expanding a charged particle beamthrough a solid angle comprising means for generating a charged particlebeam, means for accelerating said generated beam, an aperture insertedin the beam path for defining the accelerated beam, a gradient lenssystem means surrounding said defined accelerated beam for uniformlymanipulating said beam in mutually perpendicular directions toconcentrate said beam at a cross-over point posterior to said lenssystem and to form thereat a distortion free image of said aperture andexpanding said beam through a solid angle to form an enlarged uniformimage of said aperture, said gradient lens system consisting of threein-line quadrapole magnetic coupled to said accelerator means forcontaining the aperture and the lens system and means for evacuatingsaid housing means.

2. The apparatus of claim 1 wherein said housing means has wallsgenerally parallel to the accelerated beam and to each other whichextend from said acceleration means to a position approximatelycoinciding with said crossover point and which diverge at said positionto substantially parallel said beam as said beam expands after passingsaid cross-over point to form a chamber which can be substantially illedby said expanded beam.

References Cited UNITED STATES PATENTS 2,883,569 4/1959 Kaiser et al313-84 2,941,077 6/1960 Marker Z50-49.5 3,028,491 4/1962 Schleich250--49.5 3,120,609 2/ 1964 Farrell 313-84 X JAMES W. LAWRENCE, PrimaryExaminer P. C. DEMEO, Assistant Examiner U.S. Cl. X.R.

